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Electric Frenzy 05-11-2009 08:42 PM

Need some further input on EV build
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Ok, I know I sound like a broken record but I was wondering if you EV guys could help me better understand my build process.

These items I'm showing you are all hypotheticals but I'd like to see what you thought about them if they were all fabricated to work together.

The first pic is a brand new 48v golf cart motor and the second is a close ratio 6spd Harley transmission. Both items combined would be under $1k. If I were able to mate them up and throw on some good batteries wouldn't I have a pretty decent little scooter?

the reason I ask is that the motor is rated for about 13mph at 3000rpms. I figured with the trans I'd be able to string that out a lot longer while still having punchy acceleration. Am I right?

dcb 05-11-2009 09:39 PM

Sorry, me again. I was wondering about this too.

transmissions don't come free. that harley trans costs you 5 hp per here:
Six speed, HD or Baker?

The ebay auction for that motor lists it at 9.8 hp, and that may be a peak figure.

So it doesn't look like a good match.

order99 05-11-2009 10:13 PM

What top speed do you want for this scooter, and is 9.8HP a continuous or peak number? Most 48V Golf Cart motors i've seen rate between 4.5 to 5HP continuous.

I honestly don't see a problem with a fixed-gear for a scooter. Transferring that motor from a Cart chassis to a Scooter eliminates a massive amount of weight-with a Scooter you will likely have speed and torque to spare. Just play with the gear ratios until you get it right balance between smooth cruising and hill climbing.

As an example-I ran a WV 12V, 30A generator and a (borrowed)19.5V, 3.3Ahr Dewalt pack on my bicycle at a 4:1 gearing a few weeks back-I buried the needle(antique speedo only goes to 30MPH!) sprinted up a 10 degree slope and left the ground briefly at the top... :eek: When I save enough for a real 24V NiMH pack at 24V, i'll have to go 6:1 at least!

Now, that VW generator has 1HP or less at 20V...see why I think you'll have power to spare on the scoot?

Have fun!

Ryland 05-12-2009 12:32 AM

My electric car has a very similar motor to that, 48V, 6hp, 3000rpm and at 1,400 pounds + two passengers is rated to go 40mph, with out any transmission.

Electric Frenzy 05-12-2009 02:22 AM


Originally Posted by order99 (Post 103628)
Transferring that motor from a Cart chassis to a Scooter eliminates a massive amount of weight-with a Scooter you will likely have speed and torque to spare.

So let me see if I follow.

You're saying the motor is capable of much higher speeds but the weight is keeping it to just 13mph even though it's "geared" for 40mph??

A 40mph top speed is unacceptable but perhaps using a 2 speed trans would provide me the grunt I'd want off the line with a top speed more around 60mph.

dcb 05-12-2009 05:29 AM

generally speaking, for a given amount of power:

more weight=less acceleration

more drag (larger blockier shape that has to move more air)=less top speed

There will be a quiz :)

Electric Frenzy 05-12-2009 02:24 PM

no no, I understand that. What I'm trying to find out is if the 48v motor provides enough power to run at much higher speeds but it's being held back by the weight of the cart.

If that's the case then NO a trans wouldn't be needed (necessarily). It just seems to me that any motor that can only go 13mph and spin 3000rpms will need a trans to achieve 60mph (if at all possible). But what you guys are saying is that I just need to cut the weight down and make it more aerodynamic to achieve better speeds.

p.s. This is a 48v motor...I hear people saying they'll run 72v through them but not much more than that safe? How can you tell how much power a motor will hold? I thought they were rated clearly for a reason.

dcb 05-12-2009 03:16 PM

I don't have exact figures, but I recon that if ryland can go 40 with that motor, that IF you can cut your cdA (Coefficient of drag * frontal area) to half that of the citicar then you can do about 60 (assuming batteries and controller are up to it) using just sprockets (no trans maybe), but you have to use an overall ratio that is %50 greater than rylands.

If you also cut the overall weight in half for that same amount of power, your acceleration (i.e. 0 to 60) will double (how is that LiFE GB coming?).

Though it might be fun to try the two motors parallel serial shifting controller trick like the killacycle and white zombie do. So maybe design it so you can add a second motor or two wheel drive later? :)

vinny1989 05-12-2009 03:59 PM

In my mind, an electric motor and a small gearbox is a good idea. It gives you the torque and efficiency of the electric whilst retaining a decent top speed and range.

Not to mention that with a gearbox you can select the gear which keeps your motor happiest, at almost any speed.

Though, id have thought a 3 or 4 speed would be enough..

Are you having a clutch too, or direct to gearbox?

MazdaMatt 05-12-2009 04:08 PM

Don't get hung up on speed/rpm figures. That speed/rpm is for a particular vehicle and gearing. Focus more on V, I, P figures. You've got 10hp to play with - how fast does a 10hp gasoline scooter go?

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